Removing objects from an array in javascript

Question

I have this array containing simple objects

var data = [
{type:1, owner:"jason"},
{type:1, owner:"john"},
{type:2, owner:"jason"},
{type:2, owner:"alice"},
{type:2, owner:"bob"},
{type:2, owner:"clark"},
{type:1, owner:"david"}
]

i am trying to loop through the array and removing only elements with type:1. This is what i tried.

for(var i = 0; i < data.length; i++){
  if(data[i].type === 1){
     data.splice(i,1)
  }
}

Would it be stupid of me to assume that after that loop runs that all type 1 elements will be removed from the array. After running this in chrome dev tools, the array still contains {type:1, owner:"jason"} and all type:2's were left untouched as expected. what am i doing wrong?

Mritunjay · Accepted Answer · 2014-08-30 12:29:13Z

3

You have to just decrement i after splice

i--;

BTW I would like to just use filter and assign result to same data variable like bellow

data = data.filter(function(obj) {
    return obj.type !== 1;
})

console.log(data);

answered Aug 30, 2014 at 12:29

Mritunjay

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1 Comment

shanks Over a year ago

Wow! that worked like magic. Thanks @Mritunjay. I think i prefer this filter solution. Any idea how well this performs on huge large data sets?

worldask · Accepted Answer · 2014-08-30 12:31:40Z

1

you should run i-- after splice, because splice resize the array,the array index immediately changed after removing.

for(var i = 0; i < data.length; i++){
  if(data[i].type === 1){
     data.splice(i,1);
     i--;
  }
}

answered Aug 30, 2014 at 12:31

worldask

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3 Comments

keeshux Over a year ago

Index 0 must be treated differently though.

worldask Over a year ago

index 0 will be -1 after i--, but will be 0 again when current loop ends after i++.

shanks Over a year ago

thanks @worldask. guess my understanding of the splice method is limited.

Amna Irfan · Accepted Answer · 2014-08-30 13:00:11Z

1

Decrease i by 1 whenever you splice your var data. Because that means the array list of objects is becoming smaller and so the index position shifts.

Since you aren't decreasing by 1, you start with the jason at position 0 and then directly jump to jason at position 2. WHY does this happen? Since you sliced an object in the beginning, your index position shifted like this.

First loop: i=0

    var data = [
    {type:1, owner:"jason"},//position 0
    {type:1, owner:"john"},//position 1
    {type:2, owner:"jason"},//position 2
    {type:2, owner:"alice"},//position 3
    {type:2, owner:"bob"},//position 4
    {type:2, owner:"clark"},//position 5
    {type:1, owner:"david"}//position 6
    ]

Second loop i=1

    var data = [
    {type:1, owner:"jason"},//SPLICED
    {type:1, owner:"john"},// position 0
    {type:2, owner:"jason"}, //position 1
    {type:2, owner:"alice"},// position 2
    {type:2, owner:"bob"},//position 3
    {type:2, owner:"clark"},//position 4
    {type:1, owner:"david"}//position 5
    ]

answered Aug 30, 2014 at 13:00

Amna Irfan

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1 Comment

shanks Over a year ago

+1 for the explanation. This is exactly what i wanted to know. @Amna Irfan thanks :)

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